Photoconductor for electrophotography

ABSTRACT

A photoconductor for electrophotography comprises a substrate and a photosensitive layer formed on the substrate and including a novel tetrakisazo compound. The one type of the tetrakisazo compound is represented by the following general formula. ##STR1## Wherein A stands for a coupler residual group and R stands for one of a hydrogen atom, an alkyl group and an aryl group which may have a substituent group.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to photoconductors for electrophotography, and particularly to a photoconductor for electrophotography which contains a novel charge generating substance in the photosensitive layer thereof formed on an electroconductive substrate.

2. Description of the Prior Art

Photosensitive materials which have heretofore been used in photoconductors for electrophotography include inorganic photoconductive substances such as selenium and selenium alloys, dispersions of inorganic photoconductive substances such as zinc oxide and cadmium sulfide in resin binders, organic polymeric photoconductive substances such as poly-N-vinylcarbazole and polyvinylanthracene, organic photoconductive substances such as phthalocyanine compounds and bisazo compounds, dispersions of such organic photoconductive substances in resin binder, and a sputtered film of such organic photoconductive substances.

Photoconductors are required to have a function of maintaining a surface electric charge in the dark, a function of generating an electric charge upon receiving light, and a function of transporting an electric charge upon receiving light. They are classified into two types of photoconductors, namely so-called monolayer type photoconductors, and so-called laminate type photoconductors. The former comprises a single layer having all of the above-mentioned three functions, and the latter comprises functionally distinguishable laminated layers, one of which contributes mainly to the generation of electric charge, and another of which contributes to the retention of surface electric charge in the dark and the electric charge transportation upon receiving light. In an electrophotographic method using a photoconductor of the kind as mentioned above, for example, the Carlson's system is applied to image formation. The image formation according to this system comprises steps of subjecting a photoconductor in the dark to corona discharge to charge the photoconductor, illuminating the surface of the charged photoconductor with imagewise light based on a manuscript or copy bearing, e.g., letters and/or pictures to form a latent electrostatic image, developing the formed latent electrostatic image with a toner, and transferring the developed toner image to a support such as a paper sheet to fix the toner image on the support. After the toner image transfer, the photoconductor is subjected to the steps of removal of the electric charge, removal of the remaining toner (cleaning), neutralization of the residual charge with light (erasion), an so on to be ready for reuse.

Photoconductors for electrophotography in which use is made of organic materials have recently been put into practical use by virtue of the advantageous features of flexibility, thermal stability, and/or a film forming capacity. They include a photoconductor comprising poly-N-vinylcarbazole and 2,4,7-trinitrofluoren-9-on (disclosed in U.S. Pat. No. 3,484,237), a photoconductor using an organic pigment as a main component (disclosed in Japanese Patent Laid-Open No. 37,543/1972), and a photoconductor using as a main component a eutectic complex composed of a dye and a resin (disclosed in Japanese Patent Laid-Open No. 10,785/1972). A number of novel hydrazone compounds and bisazo compounds and the like have also been put into practical use for photoconductors.

Although organic materials have many advantageous features mentioned above with which inorganic materials are not endowed, however, the fact is that there have been obtained no organic materials fully satisfying all the characteristics required of a material to be used in photoconductors for electrophotography at the present. Particular problems involved in organic materials have been concerned with photosensitivity and characteristics in continuous repeated use.

SUMMARY OF THE INVENTION

An object of the present invention, which has been made in view of the foregoing, is to provide a photoconductor for electrophotography for use in copying apparatuses and printers which photoconductor includes a novel organic materials not used to date as a charge generating substance in the photosensitive layer, and has a high photosensitivity and excellent characteristics in repeated use.

In accordance with the present invention, a photoconductor for electrophotography comprises:

a substrate; and

a photosensitive layer formed on the substrate and including at least one tetrakisazo compound represented by one of the following general formulae (I), (II), (III) and (IV) as a charge generating substance: ##STR2## wherein, R stands for one of a hydrogen atom, an alkyl group and an aryl group which may have a substituent group, A stands for one of a coupler residuals represented by the following general formulae (V) to (XI) and n stands for an integer of 2 and 3; ##STR3## wherein, Z stands for a residual group which condenses with a benzen ring to form an aromatic polycyclic group of a heterocyclic group, X₁ stands for an OR₁ or an NR₂ R₃ (each of R₁, R₂ and R₃ stands for one of a hydrogen atom, an alkyl group, an aryl group and a heterocyclic group, which groups may be or not may be substituted), each of X₂ and X₅ stands for an alkyl group, an aryl group and a heterocyclic group, which groups may be or not may be substituted, each of X₃ and X₆ stands for one of a hydrogen atom, a cyano group, a carbamoyl group, a carboxyl group, an ester group and an acyl group, each of X₄ and X₁₁ stands for one of a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an aralkyl group, an aryl group and a heterocyclic group, which groups may be or not may be substituted, each of X₇ and X₈ stands for a hydrogen atom, a halogen atom, a nitro group, an alkyl group and an alkoxy group, last two of which groups may be or not may be substituted, X₉ stands for one of an alkyl group, an aryl group, a carboxyl group, an ester group, which groups may be or not may be substituted, X₁₀ stands for one of an aryl group an a heterocyclic group, both of which may be or not may be substituted, and Y stands for a residual group which forms an aromatic ring or a heterocycle.

Here, the photoconductive layer may be a monolayer including dispersion of a charge generating substance selected from tetrakisazo compounds represented by one of the general formula (I), (II), (III) and (IV) and at least one of charge transporting substances.

The photoconductive layer may comprise a laminate of a charge transporting layer mainly composed of a charge transporting substance and a charge generating layer including a charge generating substance selected from tetrakisazo compounds represented by one of the general formula (I), (II), III) and (IV).

The above and other objects, effects, features and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 to 3 are schematic cross sectional views of photoconductors according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

A photoconductor according to the present invention includes at one tetrakisazo compound represented by the following general formulae (I), (II), (III) and (IV). ##STR4##

In foregoing general formulae (I) to (IV), R stands for one of a hydrogen atom, an alkyl group and an aryl group which m ay have a substituent group, A stands for one of a coupler residuals represented by the following general formulae (V) to (XI) and n stands for an integer of 2 and 3; ##STR5##

In the general formulae (V) to (XI) Z stands for a residual group which condenses with a benzene ring to form an aromatic polycyclic group or a heterocyclic group, X₁ stands for an OR₁ or an NR₂ R₃ (each of R₁, R₂ and R₃ stands for one of a hydrogen atom, an alkyl group, an aryl group and a heterocyclic group, which groups may be or not may be substituted), each of X₂ and X₅ stands for an alkyl group, an aryl group and a heterocyclic group, which groups may be or not may be substituted, each of X₃ and X₆ stands for one of a hydrogen atom, a cyano group, a carbamoyl group, a carboxyl group, an ester group and an acyl group, each of X₄ and X₁₁ stands for one of a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an aralkyl group, an aryl group and a heterocyclic group, which groups may be or not may be substituted, each of X₇ and X₈ stands for a hydrogen atom, a halogen atom, a nitro group, an alkyl group and an alkoxy group, last two of which groups may be or not may be substituted, X₉ stands for one of an alkyl group, an aryl group, a carboxyl group, an ester group, which groups may be or not may be substituted, X_(1O) stands for one of an aryl group and a heterocyclic group, both of which may be or not may be substituted, and Y stands for a residual group which forms an aromatic ring or a heterocycle.

Tetrakisazo compounds, which include four azo groups, represented by the foregoing general formula (I) can easily be synthesized by diazotizing an amino compound represented by the following general formula (1) with a conventional method and coupling reacting obtained diazo compound with a corresponding coupler in an appropriate solvent (for example, N, N-dimethylformamide, dimethyl sulfoxide and so on) under the presence of a base. ##STR6##

In the formula (1), R stands for one of a hydrogen atom, an alkyl group and an aryl group which may have a substituent group.

Tetrakisazo compounds represented by the general formula (II) can be synthesized by diazotizing an amino compound represented by the following general formula (2) with a conventional method and coupling reacting obtained diazo compound with a corresponding coupler in an appropriate solvent (for example, N,N-dimethylformamide, dimethyl sulfoxide and so on) under the presence of a base. ##STR7##

In the formula (2), R stands for one of a hydrogen atom, an alkyl group and an aryl group which may have a substituent group and n stands for one integer of 2 and 3.

Tetrakisazo compound represented by the general formula (III) can be synthesized by diazotizing an amino compound represented by the following general formula (3) with a conventional method and coupling reacting obtained diazo compound with a corresponding coupler in an appropriate solvent (for example, N,N-dimethylformamide, dimethyl sulfoxide and so on) under the presence of a base. ##STR8##

Tetrakisazo compounds represented by the general formula (IV) can be synthesized by diazotizing an amino compound represented by the following general formula (4) with a conventional method and coupling reacting obtained diazo compound with a corresponding coupler in an appropriate solvent (for example, N,N-dimethylformamide, dimethyl sulfoxide and so on) under the presence of a base. ##STR9##

As for the use of the tetrakisazo compounds represented by the general formulae given above in photosensitive layers, there has been no precedent before. In the course of the intensive study of various organic materials as made in an attempt to achieve the above object, the present inventors conducted a number of experiments with those tetrakisazo compounds and, as a result, found that the use of such specific tetrakisazo compounds represented by the above general formulae (I) to (IV) as charge generating substances is very effective in improving electrophotographic characteristics. Based on this finding, photoconductors having high sensitivity and good repeated use characteristics are obtained.

Specific examples of the tetrakisazo compounds of the general formula (I) prepared in the above-mentioned manner include compound No. 1 to No. 69 as shown in the following table A.

                                      TABLE A                                      __________________________________________________________________________      ##STR10##                                                                     COMPOUND No.                                                                               R           A                                                      __________________________________________________________________________     1           H                                                                                           ##STR11##                                             2           H                                                                                           ##STR12##                                             3           H                                                                                           ##STR13##                                             4           H                                                                                           ##STR14##                                             5           H                                                                                           ##STR15##                                                                      ##STR16##                                             7           H                                                                                           ##STR17##                                             8           H                                                                                           ##STR18##                                             9           H                                                                                           ##STR19##                                             10          H                                                                                           ##STR20##                                             11          H                                                                                           ##STR21##                                             12          H                                                                                           ##STR22##                                             13          H                                                                                           ##STR23##                                             14          H                                                                                           ##STR24##                                             15          H                                                                                           ##STR25##                                             16          H                                                                                           ##STR26##                                             17          H                                                                                           ##STR27##                                             18          H                                                                                           ##STR28##                                             19          H                                                                                           ##STR29##                                             20          H                                                                                           ##STR30##                                             21          H                                                                                           ##STR31##                                             22          H                                                                                           ##STR32##                                             23          H                                                                                           ##STR33##                                                                     or                                                                              ##STR34##                                             24          CH.sub.3                                                                                    ##STR35##                                             25          CH.sub.3                                                                                    ##STR36##                                             26          CH.sub.3                                                                                    ##STR37##                                             27          CH.sub.3                                                                                    ##STR38##                                             28          C.sub.2 H.sub.5                                                                             ##STR39##                                             29          CH.sub.3                                                                                    ##STR40##                                             30          CH.sub.3                                                                                    ##STR41##                                             31          C.sub.2 H.sub.5                                                                             ##STR42##                                             32          CH.sub.3                                                                                    ##STR43##                                             33          CH.sub.3                                                                                    ##STR44##                                             34          C.sub.2 H.sub.5                                                                             ##STR45##                                             35          CH.sub.3                                                                                    ##STR46##                                             36          CH.sub.3                                                                                    ##STR47##                                             37          CH.sub.3                                                                                    ##STR48##                                             38          CH.sub.3                                                                                    ##STR49##                                             39          C.sub.2 H.sub.5                                                                             ##STR50##                                             40          CH.sub.3                                                                                    ##STR51##                                             41          CH.sub.3                                                                                    ##STR52##                                             42          CH.sub.3                                                                                    ##STR53##                                             43          CH.sub.3                                                                                    ##STR54##                                             44          C.sub.2 H.sub.5                                                                             ##STR55##                                             45          CH.sub.3                                                                                    ##STR56##                                             46          CH.sub.3                                                                                    ##STR57##                                                                     or                                                                              ##STR58##                                             47                                                                                          ##STR59##                                                                                  ##STR60##                                             48                                                                                          ##STR61##                                                                                  ##STR62##                                             49                                                                                          ##STR63##                                                                                  ##STR64##                                             50                                                                                          ##STR65##                                                                                  ##STR66##                                             51                                                                                          ##STR67##                                                                                  ##STR68##                                             52                                                                                          ##STR69##                                                                                  ##STR70##                                             53                                                                                          ##STR71##                                                                                  ##STR72##                                             54                                                                                          ##STR73##                                                                                  ##STR74##                                             55                                                                                          ##STR75##                                                                                  ##STR76##                                             56                                                                                          ##STR77##                                                                                  ##STR78##                                             57                                                                                          ##STR79##                                                                                  ##STR80##                                             58                                                                                          ##STR81##                                                                                  ##STR82##                                             59                                                                                          ##STR83##                                                                                  ##STR84##                                             60                                                                                          ##STR85##                                                                                  ##STR86##                                             61                                                                                          ##STR87##                                                                                  ##STR88##                                             62                                                                                          ##STR89##                                                                                  ##STR90##                                             63                                                                                          ##STR91##                                                                                  ##STR92##                                             64                                                                                          ##STR93##                                                                                  ##STR94##                                             65                                                                                          ##STR95##                                                                                  ##STR96##                                             66                                                                                          ##STR97##                                                                                  ##STR98##                                             67                                                                                          ##STR99##                                                                                  ##STR100##                                            68                                                                                          ##STR101##                                                                                 ##STR102##                                            69                                                                                          ##STR103##                                                                                 ##STR104##                                                                    or                                                                              ##STR105##                                            __________________________________________________________________________

Specific examples of the tetrakisazo compounds of the general formula (II) include compound No. 71 to No. 116 as shown in the following table B, when R of ##STR106## is a hydrogen atom.

                  TABLE B                                                          ______________________________________                                         COMPOUND                                                                       No.       n     A                                                              ______________________________________                                         71        2                                                                                     ##STR107##                                                    72        2                                                                                     ##STR108##                                                    73        2                                                                                     ##STR109##                                                    74        2                                                                                     ##STR110##                                                    75        2                                                                                     ##STR111##                                                    76        2                                                                                     ##STR112##                                                    77        2                                                                                     ##STR113##                                                    78        2                                                                                     ##STR114##                                                    79        2                                                                                     ##STR115##                                                    80        2                                                                                     ##STR116##                                                    81        2                                                                                     ##STR117##                                                    82        2                                                                                     ##STR118##                                                    83        2                                                                                     ##STR119##                                                    84        2                                                                                     ##STR120##                                                    85        2                                                                                     ##STR121##                                                    86        2                                                                                     ##STR122##                                                    87        2                                                                                     ##STR123##                                                    88        2                                                                                     ##STR124##                                                    89        2                                                                                     ##STR125##                                                    90        2                                                                                     ##STR126##                                                    91        2                                                                                     ##STR127##                                                    92        2                                                                                     ##STR128##                                                    93        2                                                                                     ##STR129##                                                                    or                                                                              ##STR130##                                                    94        3                                                                                     ##STR131##                                                    95        3                                                                                     ##STR132##                                                    96        3                                                                                     ##STR133##                                                    97        3                                                                                     ##STR134##                                                    98        3                                                                                     ##STR135##                                                    99        3                                                                                     ##STR136##                                                    100       3                                                                                     ##STR137##                                                    101       3                                                                                     ##STR138##                                                    102       3                                                                                     ##STR139##                                                    103       3                                                                                     ##STR140##                                                    104       3                                                                                     ##STR141##                                                    105       3                                                                                     ##STR142##                                                    106       3                                                                                     ##STR143##                                                    107       3                                                                                     ##STR144##                                                    108       3                                                                                     ##STR145##                                                    109       3                                                                                     ##STR146##                                                    110       3                                                                                     ##STR147##                                                    111       3                                                                                     ##STR148##                                                    112       3                                                                                     ##STR149##                                                    113       3                                                                                     ##STR150##                                                    114       3                                                                                     ##STR151##                                                    115       3                                                                                     ##STR152##                                                    116       3                                                                                     ##STR153##                                                                    or                                                                              ##STR154##                                                    ______________________________________                                    

When n in the general formula (II) equal 3 and R is as follows, compound No. 117 to No. 139 are shown in Table C.

                                      TABLE C                                      __________________________________________________________________________      ##STR155##                                                                    COMPOUND No. R          A                                                      __________________________________________________________________________     117          CH.sub.3                                                                                   ##STR156##                                            118          CH.sub.3                                                                                   ##STR157##                                            119          CH.sub.3                                                                                   ##STR158##                                            120          CH.sub.3                                                                                   ##STR159##                                            121                                                                                          ##STR160##                                                                                ##STR161##                                            122          CH.sub.3                                                                                   ##STR162##                                            123          CH.sub.3                                                                                   ##STR163##                                            124                                                                                          ##STR164##                                                                                ##STR165##                                            125          CH.sub.3                                                                                   ##STR166##                                            126          CH.sub.3                                                                                   ##STR167##                                            127                                                                                          ##STR168##                                                                                ##STR169##                                            128          CH.sub.3                                                                                   ##STR170##                                            129          CH.sub.3                                                                                   ##STR171##                                            130                                                                                          ##STR172##                                                                                ##STR173##                                            131          CH.sub.3                                                                                   ##STR174##                                            132          CH.sub.3                                                                                   ##STR175##                                            133          CH.sub.3                                                                                   ##STR176##                                            134          CH.sub.3                                                                                   ##STR177##                                            135                                                                                          ##STR178##                                                                                ##STR179##                                            136          CH.sub.3                                                                                   ##STR180##                                            137          CH.sub.3                                                                                   ##STR181##                                            138                                                                                          ##STR182##                                                                                ##STR183##                                            139          CH.sub.3                                                                                   ##STR184##                                                                    or                                                                              ##STR185##                                            __________________________________________________________________________

Specific examples of the tetrakisazo compounds represented by the general formula (III) include compound No. 141 to No. 162 as shown in the following table D.

                                      TABLE D                                      __________________________________________________________________________      ##STR186##                                                                    COMPOUND                  COMPOUND                                             No.     A                 No.     A                                            __________________________________________________________________________     141                                                                                     ##STR187##       145                                                                                     ##STR188##                                  142                                                                                     ##STR189##       146                                                                                     ##STR190##                                  143                                                                                     ##STR191##       147                                                                                     ##STR192##                                  144                                                                                     ##STR193##       148                                                                                     ##STR194##                                  149                                                                                     ##STR195##       153                                                                                     ##STR196##                                  150                                                                                     ##STR197##       154                                                                                     ##STR198##                                  151                                                                                     ##STR199##       155                                                                                     ##STR200##                                  152                                                                                     ##STR201##       156                                                                                     ##STR202##                                  157                                                                                     ##STR203##       161                                                                                     ##STR204##                                  158                                                                                     ##STR205##       162                                                                                     ##STR206##                                                                    or                                           159                                                                                     ##STR207##                                                                                               ##STR208##                                  160                                                                                     ##STR209##                                                            __________________________________________________________________________

Specific examples of the tetrakisazo compounds represented by the general formula (IV) include compound No. 171 to No. 192 as shown in the following table E.

                                      TABLE E                                      __________________________________________________________________________      ##STR210##                                                                    COMPOUND                  COMPOUND                                             No.     A                 No.     A                                            __________________________________________________________________________     171                                                                                     ##STR211##       175                                                                                     ##STR212##                                  172                                                                                     ##STR213##       176                                                                                     ##STR214##                                  173                                                                                     ##STR215##       177                                                                                     ##STR216##                                  174                                                                                     ##STR217##       178                                                                                     ##STR218##                                  179                                                                                     ##STR219##       183                                                                                     ##STR220##                                  180                                                                                     ##STR221##       184                                                                                     ##STR222##                                  181                                                                                     ##STR223##       185                                                                                     ##STR224##                                  182                                                                                     ##STR225##       186                                                                                     ##STR226##                                  187                                                                                     ##STR227##       191                                                                                     ##STR228##                                  188                                                                                     ##STR229##       192                                                                                     ##STR230##                                                                    or                                           189                                                                                     ##STR231##                                                                                               ##STR232##                                  190                                                                                     ##STR233##                                                            __________________________________________________________________________

The photoconductor of the present invention, which contains the tetrakisazo compound represented by the above-mentioned general formulae (I), (II), (III) or (IV) in the photosensitive layer thereof, may have any one of the structures as shown in FIGS. 1, 2 and 3 according to the manner of application thereto of the tetrakisazo compound.

FIGS. 1, 2 and 3 are schematic cross sectional views of different embodiments of the photoconductor of the present invention, respectively.

FIG. 1 shows a cross-sectional view of a monolayer type photoconductor. A photosensitive layer 2A is provided on an electroconductive substrate 1. The photosensitive layer 2A comprises the above-mentioned tetrakisazo compound as a charge generating substance 3, and a charge transporting substance 5 both of which substances are dispersed in a resin binder matrix so that the photosensitive layer 2A functions as a photoconductor.

FIG. 2 shows a laminate type photoconductor. A laminated photosensitive layer 2B is provided on an electroconductive substrate 1, a lower layer of the laminate is a charge generating layer 4 including the above-mentioned tetrakisazo compound as a charge generating substance 3 and an upper one is a charge transporting layer 6 containing a charge transporting substance 5 as a main component, so that the photosensitive layer 2B functions as a photoconductor. This photoconductor is usually used according to the negative charge mode.

FIG. 3 shows another laminate type photoconductor having a layer structure in reverse to that of FIG. 2. A laminated photosensitive layer 2C is provided on an electroconductive substrate 1, a lower layer of the laminate is a charge transporting layer 6 and an upper one is a charge generating layer 4 including the above-mentioned tetrakisazo compoUnd as a charge generating substance 3. The photosensitive layer also functions as a photoconductor. This photoconductor is usually used according to the positive charge mode. In this case, a covering layer 7 may generally be further provided as shown in FIG. 3 to protect the charge generating layer 4.

Thus, two kinds of layer structure are provided for laminate type photoconductors. The reason for this is that, even if any photoconductor with the layer structure as shown in FIG. 2 is to be used in the positive charge mode, no charge transporting substances adaptable to the positive charge mode have been found yet. Accordingly, when any laminate type photoconductor is to be used in the positive charge mode, the photoconductor is required of a layer structure as shown in FIG. 3 for the present.

A photoconductor as shown in FIG. 1 can be produced by dispersing a charge generating substance in a solution of a charge transporting substance and a resin binder and applying the resulting dispersion on an electroconductive substrate and then drying the resulting coating film.

A photoconductor as shown in FIG. 2 can be prepared bu applying and drying a dispersion of a particulate charge generating substance in a solvent and/or a resin binder on an electroconductive substrate, followed by applying a solution of a charge transporting substance and a resin binder on the resulting layer and prying.

A photoconductor as shown in FIG. 3 can be prepared by applying and drying a solution of a charge transporting substance and a resin binder onto an electroconductive substrate, and coating and drying dispersion of a particulate charge generating substance in a solvent and/or a resin binder onto the resulting coating layer, followed by formation of a covering layer.

The electroconductive substrate 1 serves as an electrode of the photoconductor and as a support for a layer or layers formed thereon. The electroconductive substrate may be in the form of a cylinder, a plate or a film, and may be made of a metallic material such as aluminum, stainless steel or nickel, or other material having a surface treated to be electroconductive, such as glass so treated or a resin so treated.

The charge generating layer 4 is formed by application of a dispersion of a tetrakisazo represented by the general formulae (I) to (IV) as a charge generating substance 3 in a resin binder, and this layer generates an electric charge upon receiving light. It is important that the charge generating layer 4 be high not only in charge generating efficiency but also in capability of injecting the generated electric charge into the charge transporting layer 6 and any covering layer 7, which capability is desirably as little dependent upon the electric field as possible and high even in low intensity electric fields. It also is possible to form a charge generating layer using a charge generating substance as a main component in mixture with a charge transporting substance and so on. Resin binders usable in the charge generating layer include polycarbonates, polyesters, polyamides, polyurethanes, polyvinyl chloride, epoxy resins, silicone resins, diallyl phthalate resins and homopolymers and copolymers of methacrylate esters, which may be used either alone or in appropriate combination.

The charge transporting layer 6, which is formed by application of a solution or dispersion of a hydrazone compound, a pyrazoline compound, a stilbene compound, a triphenyl-amine compound, an oxazole compound or an oxadiazole compound as an organic charge transporting substance in a resin binder, exhibits a function of serving as an insulating layer in the mark to retain an electric charge of the photoconductor as well as a function transporting an electric charge injected from the charge generating layer upon receiving light. Resin binders usable in the charge transporting layer include polycarbonates, polyesters, polyamides, polyurethanes, epoxy resins, silicone resins, and homopolymers and copolymers of methacrylate ester.

The covering layer 7 has a function of receiving and retaining an electric charge generated my corona discharge in the dark and a capability of transmitting light to which the charge generating layer should respond. It is necessary that the covering layer 7 transmits light upon exposure of the photoconductor and allows the light to reach the charge generating layer, and then undergoes the injection of an electric charge generated in the charge generating layer to neutralize and mrases a surface electric charge. Materials usable in the covering layer include organic insulating film-forming materials such as polyesters and polyamides. Such organic materials may also be used in mixture with an inorganic material such as a glass resin or Sio₂, or an electric resistance-lowering material such as a metal or a metallic oxide. Materials usable in the covering layer are not limited to organic insulating film-forming materials, and further include inorganic materials such as SiO₂, metals, and metallic oxides, which may me formed on a covering layer by an appropriate method such as vacuum evaporation and deposition, or sputtering. From the viewpoint of the aforementioned description, it is desirable that the material to be used in the covering layer be as transparent as possible in the wavelength range wherein the charge generating substance attains maximum light absorption.

Although the thickness of the covering layer depends on the material or composition thereof, it can be arbitrarily set in so far as it does not produce any adverse effects including an increase in a residual potential in continuous repeated use.

Examples will now be given, wherein various compounds represented by the general formulae (I) to (IV) were respectively used to produce photoconductors.

EXAMPLE 1

50 marts my weight of the tetrakisazo compound No. 1, 100 parts by weight of a polyester resin (Vylon 200, manufactured by Toyobo Co., Ltd.) and 100 marts my weight of 1-phenyl-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)- 2-pyrazoline (ASPP) are kneaded with tetrahydrofuran (THF) as a solvent with a mixer for 3 hours to prepare a coating liquid. The coating liquid was applied onto an aluminum-deposited polyester film (Al-PET) s mn electroconductive substrate my means of the wire mar technique to form a photosensitive layer having a dry thickness of 15 μm. Thus, a photoconductor with the structure shown in FIG. 1 was produced.

EXAMPLE 2

First, 100 parts by weight of p-diethylaminobenzaldehyde-diphenylhydrazone (ABPH) and 100 parts by weight of polycarbonate resin (Panlite L-1250 manufactured by Teijin in chemicals Co., Ltd.) were solved in methylene chloride to prepare a coating liquid. The coating liquid was applied onto an aluminum-deposited polyester film substrate by the wire mar technique to form a charge transporting layer having a dry thickness of 15 μm. 50 parts my weight of the compound No. 2 and 50 parts by weight of a polyester resin (Vylon 200 ) were kneaded with a mixer for 3 hours together with THF as a solvent to prepare a coating liquid, which was then applied onto the charge transporting layer my the wire mar technique to form a charge generating layer having a dry thickness of 0.5 μm. Thus, a photoconductor with a structure corresponding to that shown in FIG. 3 was produced. The covering layer, which is not directly related to the present invention was not provided.

EXAMPLE 3

A charge transporting layer was formed in substantially the same manner as in Example 2 except that α-phenyl-4'-N,N-dimethylaminostilbene, which is a stilbene compound, was used to replace ABPH as a charge transporting substance. Then a charge generating layer was formed on the charge transporting layer, thus a photoconductor was produced.

EXAMPLE 4

A charge transporting layer was formed in substantially the same manner as in Example 2 except that tri(p-tolyl)amine, which is a triphenylamine compound, was used to replace ABPH as a charge transporting substance. Then a charge generating layer was formed on the charge transporting layer, thus a photoconductor was produced.

EXAMPLE 5

A charge transporting layer was formed in substantially the same manner as in Example 2 except that 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole, which is an oxadiazole compound, was used to replace ABPH ms m transporting substance. Then a charge generating layer was formed on the charge transporting layer, thus a photoconductor was produced.

The electrophotographic characteristics of the photoconductors thus produced were measured by utilizing an electrostatic recording paper testing apparatus (Kawaguchi Denki model SP-428). The result obtained are shown in Table 1.

The surface potential V_(s) (volts) of each photoconductor is an initial surface potential which was measured when the surface of the photoconductor was positively charged in the dark by corona discharge at +6.0 kV for 10 seconds. After the discontinuation of the corona discharge, the photoconductor was allowed to stand in the dark for 2 seconds, after which the surface potential V_(d) (volts) of the photoconductor was measured. subsequently, the surface of the photoconductor was irradiated with white light at an illuminance of 2 luxes and the time (seconds) required for the irradiation to decrease the surface potential of the photoconductor to half of the V_(d) was measured. then from which the half decay exposure amount E_(1/2) (lux·sec) was calculated. Also, the surface potential of the photoconductor after 10 seconds of irradiation thereof with white light at an illuminance of 2 luxes was measured as a residual potential V_(r) (volts).

                  TABLE 1                                                          ______________________________________                                                  Vs        Vr      E1/2                                                         (volt)    (volt)  (lux · sec)                                ______________________________________                                         Example 1  660         50      5.3                                             Example 2  650         50      4.3                                             Example 3  600         40      5.6                                             Example 4  670         70      4.4                                             Example 5  700         50      5.9                                             ______________________________________                                    

As can be seen in Table 1, the photoconductors of Examples 1 to 5 have good characteristics in the half decay exposure amounts E_(1/2) and the residual potentials V_(r).

EXAMPLE 6

100 parts my weight of each of respective tetrakisazo compounds Nos. from 3 to 69 and 100 parts by Weight of polyester resin (Vylon 200) were kneaded with THF as a solvent with a mixer for 3 hours to prepare a coating liquid. The respective coating liquids were applied onto aluminum substrates to form a charge generating layer having a dry thickness of about 0.5 μm. Further, the coating liquid of ABPH prepared in substantially the same manner as in Example 2 was applied on the respective charge generating layer having a thickness of about 15 μm, thus photoconductors were produced.

The electrophotographic characteristics of the photoconductors thus produced were measured by utilizing an electrostatic recording paper testing apparatus sp-428. The results of the measurements are shown in Table 2.

The surface potential V_(s) (volts) of each photoconductor is an initial surface potential which was measured when the surface of the photoconductor was positively charged in the dark by corona discharge at -6.0 kV for 10 seconds. After the discontinuation of the corona discharge, the photoconductor was allowed to stand in the dark for 2 seconds, after which the surface potential V_(d) (volts) of the photoconductor was measured. Subsequently, the surface of the photoconductor was irradiated with white light at an illuminance of 2 luxes and the time (seconds) required for the irradiation to decrease the surface potential of the photoconductor to half of the V_(d) was measured, then from which the half decay exposure amount E_(1/2) (lux·sec was calculated.

As can me seen in Table 2, the photoconductors using the tetrakisazo compound Nos. 3 to 69 as a charge generating substance have good characteristics in the half decay exposure amount E_(1/2).

                  TABLE 2                                                          ______________________________________                                         Compound  E1/2        Compound  E1/2                                           NO.       (lux · sec)                                                                       No.       (lux · sec)                           ______________________________________                                          3        7.3         15        8.9                                             4        4.5         16        6.0                                             5        5.9         17        8.3                                             6        5.1         18        7.3                                             7        4.9         19        6.5                                             8        5.1         20        4.4                                             9        5.4         21        5.6                                            10        4.4         22        4.1                                            11        7.2         23        7.8                                            12        6.6         24        5.7                                            13        4.8         25        5.5                                            14        6.5         26        4.9                                            27        4.3         44        5.5                                            28        5.8         45        6.8                                            29        5.2         46        5.2                                            30        7.8         47        5.4                                            31        6.3         48        4.0                                            32        4.9         49        5.3                                            33        7.5         50        5.1                                            34        6.3         51        6.6                                            35        7.5         52        5.3                                            36        8.3         53        4.7                                            37        4.9         54        6.9                                            38        6.1         55        7.2                                            39        5.7         56        5.3                                            40        5.6         57        7.1                                            41        4.6         58        4.4                                            42        4.3         59        7.8                                            43        6.1         60        6.3                                            61        5.6         66        6.7                                            62        4.7         67        8.0                                            63        8.1         68        8.7                                            64        7.6         69        4.9                                            65        6.6                                                                  ______________________________________                                    

EXAMPLE 7

50 parts mm weight of the tetrakisazo compound No. 71, 100 parts by weight of a polyester resin (Vylon 200) and 100 parts by weight of 1-phenyl-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)-2pyrazoline (ASPP) are kneaded with tetrahydrofuran (THF) as a solvent with a mixer for 3 hours to prepare a coating liquid. The coating liquid was applied onto an aluminum deposited polyester film Al- PET) as an electroconductive substrate my means of the wire mar technique to form a photosensitive layer having a dry thickness of 15 μm. Thus a photoconductor with the structure shown in FIG. 1 was produced.

EXAMPLE 8

100 parts by weight of p-diethylaminobenzaldehyde-diphenylhydrazone (ABPH) and 100 parts by weight of polycarbonate resin (Panlite L-1250) were solved in methylene chloride to prepare a coating liquid. The coating liquid was applied onto an aluminum-deposited polyester film substrate by the wire bar technique to form a charge transporting layer having a dry thickness of 15 μm. 50 parts my weight of the compound No. 72 and 50 parts my weight of a polyester resin (Vylon 200) were kneaded with a mixer for 3 hours together with THF as a solvent to prepare a coating liquid, which was then applied onto the charge transporting layer by the wire bar technique to form a charge generating layer having a dry thickness of 5 μm. Thus, a photoconductor with a structure corresponding to that shown in FIG. 3 was produced. The covering layer, which is not directly related to the present invention was not provided.

EXAMPLE 9

A charge transporting layer was formed in substantially the same manner as in Example 8 except that α-phenyl-4'-N,N-dimethylaminostilbene was used to replace ABPH as a charge transporting substance. Then a charge generating layer was formed on the charge transporting layer, thus a photoconductor was produced.

EXAMPLE 10

A charge transporting layer was formed in substantially the same manner as in Example 8 except that tri(p tolyl)amine was used to replace ABPH as a charge transporting substance. Then a charge generating layer was formed on the charge transporting layer, thus a photoconductor was produced.

EXAMPLE 11

A charge transporting layer was formed in substantially the same manner as in Example 8 except that 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole was used to replace ABPH as a charge transporting substance. Then a charge generating layer was formed on the charge transporting layer, thus a photoconductor was produced.

The electrophotographic characteristics of the photoconductors thus produced were measured in the same manner as in Examples 1 to 5 by utilizing an electrostatic recording paper testing apparatus Model SP-428. The result obtained are shown in Table 3.

                  TABLE 3                                                          ______________________________________                                                  Vs        Vr      E1/2                                                         (volt)    (volt)  (lux · sec)                                ______________________________________                                         Example 7  620         50      4.2                                             Example 8  650         40      5.8                                             Example 9  640         50      6.3                                             Example 10 630         50      5.2                                             Example 11 700         70      5.3                                             ______________________________________                                    

As can me seen in Table 3, the photoconductors of Examples 7 to 11 have good characteristics in the half decay exposure amounts E_(1/2) and the residual potentials V_(r).

EXAMPLE 12

100 parts by weight of each of respective tetrakisazo compounds Nos. from 73 to 139 and 100 parts by weight of polyester resin (Vylon 200) were kneaded with THF ms a solvent with a mixer for 3 hours to prepare a coating liquid. The respective coating liquids were applied onto aluminum substrates to form a charge generating layer having a dry thickness of about 0.5 μm. Further, the coating liquid of ABPH prepared in substantially the same manner as in Example 8 was applied on the respective charge generating layer having a thickness of about 15 μm, thus photoconductors were produced.

The electrophotographic characteristics of the photoconductors thus produced were measured by utilizing an electrostatic recording paper testing apparatus SP-428 and in the same manner as in Example 6. The results of the measurements are shown in Table 4.

As can be seen in Table 4, the photoconductors using the tetrakisazo compound Nos. 73 to 139 as a charge generating substance have good characteristics in the half decay exposure amount E_(1/2).

                  TABLE 4                                                          ______________________________________                                         Compound  E1/2        Compound  E1/2                                           NO.       (lux · sec)                                                                       No.       (lux · sec)                           ______________________________________                                          73       4.6          90       4.5                                             74       4.8          91       5.6                                             75       4.6          92       4.4                                             76       5.2          93       4.9                                             77       3.1          94       5.0                                             78       5.7          95       5.0                                             79       6.4          96       3.9                                             80       6.3          97       4.1                                             81       8.4          98       5.9                                             82       5.0          99       5.1                                             83       6.4         100       4.4                                             84       6.4         101       5.4                                             85       4.8         102       5.2                                             86       5.7         103       7.6                                             87       5.1         104       6.8                                             88       4.0         105       6.5                                             89       5.8         106       6.9                                            107       5.8         124       6.9                                            108       5.2         125       6.2                                            109       4.6         126       5.6                                            110       5.8         127       7.8                                            111       4.9         128       6.4                                            112       4.5         129       7.9                                            113       6.9         130       6.1                                            114       7.5         131       4.7                                            115       6.5         132       6.0                                            116       3.7         133       7.3                                            117       5.4         134       7.3                                            118       3.9         135       6.5                                            119       4.9         136       6.4                                            120       5.4         137       8.6                                            121       6.7         138       4.1                                            122       4.3         139       5.8                                            123       5.7                                                                  ______________________________________                                    

EXAMPLE 13

50 parts by weight of the tetrakisazo compound No. 141, 1 Q parts by weight of a polyester resin (Vylon 200) and 100 parts weight of 1-phenyl-3-(p-diethylaminostryryl)-5-(p-diethylaminophenyl)-2-pyrazoline (ASPP) are kneaded with tetrahydrofuran (THF) as a solvent with a mixer for 3 hours to prepare a coating liquid. The coating liquid was applied onto an aluminum-deposited polyester film (Al-PET) as an electroconductive substrate by means of the wire mar technique to form a photosensitive layer having a dry thickness of 15μm. Thus, a photoconductor with the structure shown in FIG. 1 was produced.

EXAMPLE 14

100 parts my weight of p-diethylaminobenzaldehyde-diphenylhydrazone (ABPH) and 100 parts my weight of polycarbonate resin (Panlite t-1250) were solved in methylene chloride to prepare a coating liquid. The coating liquid was applied onto an aluminum-deposited polyester film substrate by the wire bar technique to form a charge transporting layer having a dry thickness of 15 μm. 50 parts by weight of the compound No. 142 and 50 parts my weight of a polyester resin (Vylon 200) were kneaded with a mixer for 3 hours together with THF as a solvent to prepare a coating liquid, which was then applied onto the charge transporting layer my the wire mar technique to form a charge generating layer having a dry thickness of 0.5 μm. Thus, a photoconductor with a structure corresponding to that shown in FIG. 3 was produced. The covering layer, which is not directly related to the present invention was not provided.

EXAMPLE 15

A charge transporting layer was formed in substantially the same manner as in Example 14 except that α-phenyl-4'-N,N-dimethylaminostilbene was used to replace ABPH as a charge transporting substance. Then a charge generating layer was formed on the charge transporting layer, thus a photoconductor was produced.

EXAMPLE 16

A charge transporting layer was formed in substantially the same manner as in Example 14 except that tri(p tolyl)amine was used to replace ABPH as a charge transporting substance. Then a charge generating layer was formed on the charge transporting layer, thus a photoconductor was produced.

EXAMPLE 17

A charge transporting layer was formed in substantially the samm manner as in Example 14 except that 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole was used to replace ABPH as a charge transporting substance. Then a charge generating layer was formed on the charge transporting layer, thus a photoconductor was produced.

The electrophotographic characteristics of the photoconductors thus produced were measured by utilizing an electrostatic recording paper testing apparatus Model SP-428 and in the same manner as in Examples 1 to 5. The result obtained are shown in Table 5.

                  TABLE 5                                                          ______________________________________                                                  Vs        Vr      E1/2                                                         (volt)    (volt)  (lux · sec)                                ______________________________________                                         Example 13 620         80      4.8                                             Example 14 660         70      5.2                                             Example 15 650         60      5.3                                             Example 16 630         70      6.4                                             Example 17 670         40      5.5                                             ______________________________________                                    

As can me seen in Table 5, the photoconductors of Examples 13 to 17 have good characteristics in the half decay exposure amounts E_(1/2) and the residual potentials V_(r).

EXAMPLE 18

100 parts by weight of each of respective tetrakisazo compounds Nos. from 143 to 162 and 100 parts by weight of polyester resin (Vylon 200) were kneaded with THF as a solvent with a mixer for 3 hours to prepare a coating liquid. The respective coating liquids were applied onto aluminum substrates to form a charge generating layer having a dry thickness of about 0.5 μm. Further, the coating liquid of ABPH prepared in substantially the same manner as in Example 14 was applied on the respective charge generating layer having a thickness of about 15 μm, thus photoconductors were produced.

The electrophotographic characteristics of the photoconductors thus produced were measured by utilizing an electrostatic recording paper testing apparatus SP-428 and in the same manner as in the Example 6. The results of the measurements are shown in Table 6.

As can me seen in Table 6, the photoconductors using the tetrakisazo compound Nos. 143 to 162 as a charge generating substance have good characteristics in the half decay exposure amount E_(1/2)

                  TABLE 6                                                          ______________________________________                                         Compound  E1/2        Compound  E1/2                                           NO.       (lux · sec)                                                                       No.       (lux · sec)                           ______________________________________                                         143       5.2         153       8.1                                            144       6.6         154       6.4                                            145       4.8         155       5.1                                            146       5.1         156       4.1                                            147       8.6         157       5.9                                            148       6.7         158       5.1                                            149       6.1         159       3.9                                            150       4.9         160       8.2                                            151       4.8         161       7.1                                            152       6.1         162       5.3                                            ______________________________________                                    

EXAMPLE 19

50 parts my weight of the tetrakisazo compound No. 171, 100 parts by weight of a polyester resin (Vylon 200) and 100 parts by weight of 1-phenyl-3-(p-diethylaminostyryl)-5-(p-diethylaminophenyl)-2-pyrazoline (ASPP) are kneaded with tetrahydrofuran (THF) as a solvent with a mixer for 3 hours to prepare a coating liquid. The coating liquid was applied onto an aluminum-deposited polyester film (Al-PET) as an electroconductive substrate by means of the wire mar technique to form a photosensitive layer having a dry thickness of 15 μm. Thus, a photoconductor with the structure shown in FIG. 1 was produced.

EXAMPLE 20

100 parts by weight of p-diethylaminobenzalhehyde-diphenylhydrazone (ABPH) and 100 parts by weight of polycarbonate resin (Panlite t-1250) were solved in methylene chloride to prepare a coating liquid. The coating liquid was applied onto an aluminum-deposited polyester film substrate by the wire bar technique to form a charge transporting layer having a dry thickness of 15 μm. 50 parts my weight of the compound No. 172 and 50 parts y weight of a polyester resin (Vylon 200) were kneaded with a mixer for 3 hours together with THF as a solvent to prepare a coating liquid, which was then applied onto the charge transporting layer by the wire bar technique to form a charge generating layer having a dry thickness of 0.5 μm. Thus, a photoconductor with a structure corresponding to that shown in FIG. 3 was produced. The covering layer, which is not directly related to the present invention was not provided.

EXAMPLE 21

A charge transporting layer was formed in substantially the same manner as in Example 20 except that α-phenyl-4'-N,N-dimethylaminostilbene was used to replace ABPH as a charge transporting substance. Then a charge generating layer was formed on the charge transporting layer, thus a photoconductor was produced.

EXAMPLE 2

A charge transporting layer was formed in substantially the same manner as in Example 20 except that tri(p-tolyl)amine was used to replace ABPH as a charge transporting substance. Then a charge generating layer was formed on the charge transporting layer, thus a photoconductor was produced.

EXAMPLE 23

A charge transporting layer was formed in substantially the same manner as in Example 20 except that 2,5-bis(p-diethylaminophenyl)-1,3,4-oxadiazole was used to replace ABPH as a charge transporting substance. Then a charge generating layer was formed on the charge transporting layer, thus a photoconductor was produced.

The electrophotographic characteristics of the photoconductors thus produced were measured in the same manner as in Examples 1 to 5 by utilizing an electrostatic recording paper testing apparatus Model SP-428. The result obtained are shown in Table 7.

                  TABLE 7                                                          ______________________________________                                                  Vs        Vr      E1/2                                                         (volt)    (volt)  (lux · sec)                                ______________________________________                                         Example 19 630         80      5.5                                             Example 20 670         50      4.9                                             Example 21 650         70      5.9                                             Example 22 650         80      6.2                                             Example 23 700         50      4.7                                             ______________________________________                                    

As can e seen in Table 7, the photoconductors of Examples 19 to 23 have good characteristics in the half decay exposure amounts E_(1/2) and the residual potentials V_(r).

EXAMPLE 24

100 parts my weight of each of respective tetrakisazo compounds Nos. from 173 to 192 and 100 parts by weight of polyester resin (Vylon 200) were kneaded with THF as a solvent with a mixer for 3 hours to prepare a coating liquid. The respective coating liquids were applied onto aluminum substrates to form a charge generating layer having a dry thickness of about 0.5 μm. Further, the coating liquid of ABPH prepared in substantially the same manner as in Example 20 was applied on the respective charge generating layer having a thickness of about 15 μm, thus photoconductors were produced.

The electrophotographic characteristics of the photoconductors thus produced were measured in the same manner as in Example 6 by utilizing an electrostatic recording paper testing apparatus SP-428. The results of the measurmments are shown in Table 8.

As can e seen in Table 8, the photoconductors using the tetrakisazo compound Nos. 173 to 192 as a charge generating substance have good characteristics in the half decay exposure amount E_(1/2).

                  TABLE 8                                                          ______________________________________                                         Compound  E1/2        Compound  E1/2                                           NO.       (lux · sec)                                                                       No.       (lux · sec)                           ______________________________________                                         173       5.0         183       7.4                                            174       6.1         184       5.5                                            175       6.3         185       4.1                                            176       6.9         186       5.6                                            177       5.5         187       5.4                                            178       5.1         188       5.5                                            179       7.1         189       6.1                                            180       7.7         190       6.3                                            181       8.3         191       6.7                                            182       6.2         192       4.9                                            ______________________________________                                    

As described above, according to the present invention, since a tetrakisazo compound represented by any one of the aforementioned chemical formulae is used as a charge generating substance in a photosensitive layer formed on an electroconductive substrate, a photoconductor shows a high sensitive and excellent characteristics in repeated use when adapted to either a positive charge mode or a negative charge mode. If necessary. a covering layer may be provided on the surface of a photoconductor to improve the durability thereof.

The invention has been described in detail with respect to preferred embodiments, and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and it is the invention, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit of the invention. 

What is claimed is:
 1. A photoconductor for electrophotography comprising:a substrate; and a photosensitive layer formed on said substrate and including at least one tetrakisazo compound represented by one of the following general formulae (I), (II), (III) and (IV) as a charge generating substance: ##STR234## wherein, R stands for one of a hydrogen atom, an alkyl group and an aryl group which may have a substituent group, A stands for one of a coupler residuals represented by the following general formulae (V) to (XI) and n stands for an integer of 2 and 3; ##STR235## wherein, Z stands for a residual group which condenses with a benzen ring to form an aromatic polycyclic group or a heterocyclic group, X₁ stands for an OR₁ or an NR₂ R₃ (each of R₁, R₂ and R₃ stands for one of a hydrogen atom, an alkyl group, an aryl group and a heterocyclic group, which groups may be or not may be substituted), each of X₂ and X₅ stands for an alkyl group, an aryl group and a heterocyclic group, which groups may de or not may be substituted, each om X₃ and X₆ stands for one of a hydrogen atom, a cyano group, a carbamoyl group, a carboxyl group, an ester group and an acyl group, each of X₄ and X₁₁ stands for one of a hydrogen atom, an alkyl group, a cycloalkyl group, an alkenyl group, an aralkyl group, an aryl group and a heterocyclic group, which groups may be or not may be substituted, each of X₇ and X₈ stands for a hydrogen atom, a halogen atom, a nitro group, an alkyl group and an alkoxy group, last two of which groups may be or not may be substituted, X₉ stands for one of an alkyl group, an aryl group, a carboxyl group, an ester group, which groups may me or not may be substituted, X₁₀ stands for one of an aryl group and a heterocyclic group, moth of which may me or not may me substituted, and Y stands for a residual group which forms an aromatic ring or a heterocycle.
 2. A photoconductor as claimed in claim 1, wherein said photoconductive layer is a monolayer including dispersion of a charge generating substance selected from tetrakisazo compounds represented by one of said general formula (I), (II), (III) and (IV) and at least one of charge transporting substances.
 3. A photoconductor as claimed in claim 1, wherein said photoconductive layer comprises a laminate of a charge transporting layer mainly composed of a charge transporting substance and a charge generating layer including a charge generating substance selected from tetrakisazo compounds represented by one of said general formula (I), (II), (III) and (IV). 